Reinforced electrical contact

ABSTRACT

Improved contact pressure on power blades of an electrical cap is provided by an electrical contact formed to accept power blades in two orientations at right angles. The contact is made of a strip of metal of high conductivity and low spring properties and is reinforced by a metal clip of lower conductivity and higher spring properties of a general &#39;&#39;&#39;&#39;U&#39;&#39;&#39;&#39; configuration.

I United States Patent [151 3,662,324 Schumacher May 9, 1972 54]REINFORCED ELECTRICAL CONTACT FOREIGN PATENTS OR APPLICATIONS [72]Inventor: Walter C- S h m h W k, R 1,487,407 2/1966 Germany ..339/259 F[73] Assignee: General Electric Company Primary E.\'ammerMarvin A.Champion [22] Flled: 1971 Assistant Examiner-Robert A. Hafer [21] Appl.No.: 111,020 Attorney-Paul E. Rochford, Frank L. Neuhauser, Oscar B.

Waddell and Joseph B. F orman [52] US. Cl. ..339/255 R, 339/259 R 7 T T[51] lnt.Cl ..l-l0lr ll/22 [5 1 ABS RAC [58] Field of Search ..339/252,253, 255, 256, 259, Improved contact pressure on power blades of anelectrical /2 I 165.217 cap is provided by an electrical contact formedto accept power blades in two orientations at right angles, The contactis [56] References cued made of a strip of metal of high conductivityand low spring UNITED STATES PATENTS properties and is reinforced by ametal clip of lower conductivity and higher spring properties of ageneral U configural,969,99l 8/1934 Robinson ..339/259 X i 1,990,0872/1935 Nichols et al. 3,032,736 5/1962 Howells ..339/14 R 1 Claim, 5Drawing Figures PATENTEDHM 9 I912 3, 662,324

In yen/or [Ha/fer C Scfiumacher Afforn REINFORCED ELECTRICAL CONTACT Thepresent invention relates to an electrical wiring device and moreparticularly to a wiring device having electrical contacts of strongprong retaining capability.

The effectiveness of a wiring device for its intended purpose ofconveniencing the temporary making and subsequent breaking of electricalconnections has been developed to a degree where electrical outlets areprovided in most buildings having electrical service. Heavier andheavier currents are available from such outlets for normal household,factory and institutional use as equipment requiring heavier temporarysupply of electrical current and greater reliability of supply ofcurrent have come into more common use.

Reliability of connection is ensured by use of the locking device typeof electrical connector but special electrical caps and receptacles mustbe provided and these must have specially shaped power blades andreceiving connectors.

Greater reliability of maintained connection can be ensured in part byincreasing the retentive pressure exerted on a prong by the prongreceiving contacts of an electrical connector. However, it is known thatmaterials which have greater capability to conduct electricity willgenerally have poorer physical and work resistance properties.

One difficulty resulting from the poorer mechanical properties of highlyconductive metals used in electrical receptacles is the tendency of thecontacts to be sprung by the repeated insertion of the power blades asrequired to make electrical contact. This is familiar to most personswho have used convenience outlets in older homes. As the contact fingersof conventional convenience outlets are sprung there is a tendency toemploy power blades of greater thickness to ensure contact. This has atendency to cause further spreading of contact fingers and can cause theseparation of the contact fingers of new convenience outlets beyond thatsatisfactory for retaining the thinner power blades under acceptableblade retaining pressure. Poor contact results in heating of theconnection. As heating results in oxidation, resistance at the contactis increased and the heating effect is further increased. Hazardousheating under higher loads can result.

While it is highly desirable that the spacing between contact fingers ofa convenience outlet remain essentially constant and that the contactpressure exerted on blades inserted between the fingers not diminish dueto prolonged usage or due to use of blades of first greater andsubsequently of lesser thickness, it will be appreciated that too greata contact pressure can also be detrimental. This is particularly sowhere the metal of the contact fingers is sufficiently hard as to causea scoring or cutting of the surface of the blades inserted between thecontact fingers. Also, too great a pressure between the contact fingerscan require use of an excessive pressure to insert the power blades.This, in turn, can cause too great a pressure of the contact on thehousing and can cause deforming or even a breaking of the housingitself.

Similarly where the inserted power blade is held between contact fingerswith excessive pressure the withdrawal of the connector can causeexcessive force to be used on the current carrying cable attached to theconnector. Safety considerations require that the connector bedisconnected when the connector or cord is pulled with a force which isreasonable for the intended usage. I

Accordingly, for reliable and safe use the attainment of a contactpressure required for a convenience outlet, such as is described above,is preferably the result of developing between the contact fingers aspring pressure which does not change under repeated cycling with powerblades of different thickness.

The National Electrical Manufacturers Association has establishedstandards of blade retention known in the wiring device industry as NEMAstandards.

The prescribed standards include the capability of a fingered contact todevelop sufficient spring pressure on a smooth steel blade having athickness of 0.055 inch to hold the blade in the grip of the fingeredcontact under a pull of 1.5 pounds for 60 seconds after said contact hasbeen subjected to 20 conditioning .cycles comprising the insertion andwithdrawal of a smooth steel blade without holes having a thicknessbetween 0.073 to 0.075 inch. This standard is that specified by theNational Electrical Manufacturers Association NEMA Standards,Publication No. WD2-l963. According to Federal Specification W-C 596 b(GSAFSS) of Oct. 22, 1967 the finish on power blades used in such testsmust be an 8 microinch finish grind in a direction normal to thedirection of insertion of the blades.

A copending application of the same assignee to which this applicationis assigned Ser. No. 871,415 filed Sept. 16, 1968 teaches the formationof a NEMA contact employing an alloy of beryllium in copper. While thecontacts formed by this method have the highly desirable propertiestaught in the application, their cost is high in comparison to contactsand receptacles which do not meet the NEMA standards.

It is accordingly an object of the present invention to provide anelectrical contact which meets the NEMA standards.

It is another object of the present invention to provide an electricalcontact strip which has the desirable high spring contacts at thefingered end portion thereof but which also has an easily broken offcircuit separating tab at the mid-portion thereof.

Another object of the present invention is to provide a low cost contactand contact strip which meets the NEMA standards.

Still another object of the present invention is to provide a reinforcedcontact for a receptacle which fits into the existing housing of outletsby a reinforcement of the contact which consumes a minimum of space.

Other objects will be in part apparent and in part pointed out in thedescription which follows.

In one of its broader aspects the objects of this invention are achievedby providing an electrical contact comprising a contact strip of metalof high conductivity and low spring properties, said strip having threecontact fingers extending up from a common base to provide two contactslots in T formation, two fingers of said contact being parallel to thebase of the T and on opposite sides thereof and a third or cross fingerbeing parallel to the cross member of the T and disposed above saidcross member, a spring reinforcing clip for said contact, said clipbeing generally U-shaped, one upright of said U embracing the crossfinger of saidcontact and having its upper end bent inwardly to bearagainst an upper portion of said cross finger, the other upright of saidU being forked at its upper portion and the upper end of said fork beingbent inwardly to engage the outer surfaces of said parallel fingers toadd spring bias to resist the spread of said fingers.

The manner of achievement of the above objects will be better understoodby reference to the accompanying drawings in the description whichfollows wherein:

FIG. 1 is an exploded view of a receptacle of the present inventionshowing the relation of a spring clip to the contact strip.

FIG. 2 is a top plan view of the receptacle showing the clip in place onthe contact fingers.

FIG. 3 is a vertical section taken along the line 3-3 of FIG. 2 andshowing power blades in place in the receptacle.

FIG. 4 is a detailed perspective view of a form of clip as used in thisinvention prior to bending into form for use.

FIG. 5 is a'perspective view of the clip of FIG. 4 after being bent intoform for use.

Referring first now to FIG. 1, the several parts of a conventionalreceptacle are seen.

This includes the base 10, contact strip 12, mounting strap 14, and topor cover 16.

One of the contact strips is shown with its reinforcing clips providedpursuant to this invention in place in base 10.

The other contact strip is seen in its exploded position poised abovethe cavity into which it fits in base 10. One clip is in place at theupper contact and the other clip is shown in its exploded positionbetween the contact with which it is as sociated and the cavity intowhich the clip reinforced contact fits.

Above both the base and contact strip the mounting strap is disposed todisplay the parts thereof and its relation to the receptacle base aswell as the cover.

The base has the conventional array of parts and in fact one feature ofthe present invention is that improved receptacle performance can beachieved for receptacles of conventional construction withoutmodification of the molded plastic or of the formed metal parts butsimply by use in conjunction with an existing receptacle of uniquereinforcing spring clips.

Accordingly, base 10 is a molded base of a conventional receptacle andis used without modification in connection with the present invention.Base 10 has four cavities, two of which are elongated longitudinallyextending cavities and 22 into which contact strips 12 and 24 areinsertable.

These cavities have conventional side and bottom openings and internalribs and other configuration which receives the contact strips and holdsthem securely during use of the receptacle.

The two other cavities are grounding cavities 26 and 28. Contact 30 ofmounting strap 14 fits into cavity 26 so that grounding blades receivedthrough blade port 32 of cover 16 are accommodated in the receptacle.

- Similarly grounding port 34 of cover 16 receives grounding blades andthese blades pass into cavity 28 of base 10 contacting grounding contact36.

Turning now to contact strip 12 it is evident that this strip has aconventional form having fingered blade contacts at each end, two wireterminals 38 and 40 adjoining the end blade contacts and having a breakoff tab 42 at the mid-section of the strip.

The mounting strap 14 has screw holes 44 and 46 at each end for screwsused in mounting the assembled device into a wall box. Conventionalplaster ears, and holes for assembly screws are also incorporated in thestrap. Grounding wires may be attached at screw terminals formed ingrounding tabs 50 and 52 as needed.

Cover 16 has two pairs of power blade entry ports 54 and 56. Each pairhas a single parallel slot and a slot in T form with the cross member ofthe T parallel to the parallel slot. Power blades are inserted in pairsinto these pairs of slots, each blade pair being either alligned inparallel relation or at right angles.

The action of the reinforcing clips of this invention in improving thegripping action of the contacts on power blades inserted into contacttherewith is described with reference to FIGS. 2, 3, and 4.

Referring first to FIG. 4 one form of reinforcing spring clip usable inconnection with this invention is illustrated. The clip has a uniquecapability of reinforcing the contact fingers alligned to receive theparallel blades i.e., the blades lying generally parallel to thelongitudinal axis of the receptacle as well as the perpendicular blades,i.e., the blades the lateral extent of which is positioned generallyperpendicular to the longitudinal axis of the receptacle.

The clip as illustrated in FIG. 4 is in an open position in whichmounting on a contact strip is facilitated and may be done with handpressure. After mounting on the strip, the clip fits into the cavity byan interference fit so that as it is pressed into the cavity it closesabout and comes into position to exert spring pressure on the blades.

The form of the clip as it is aligned after being pressed into the baseis seen in FIG. 5.

Referring now to FIG. 5, the clip is seen to have a general U formationwith each of the uprights of the U bent inward at their upper portions.The base 60 of the U is generally flat to match the flat bottom of thecavities in the receptacle base and the fiat configuration of the bottomof the fingered contacts at each end of strip 12 of FIG. 1. The righthand upright 62 reinforces the finger which receives the parallel blade.

This reinforcement is evident in FIG. 3 for example where base 60 isseen bottomed in the cavity of base 10 and upright 62 rises between thelower part 82 of finger 84 and the insulating wall 86 of base 10.

An upper part 64 of the clip is bent in to bear against the upperportion of finger 84 and to urge it toward the opposing upright of theclip.

T e manner in which the finger such as 84 bears against a parallel bladeunder the urging of a clip is seen in the right hand portion of the FIG.3. Blade is shown inserted in place and bearing against the verticaledges 92 of the fingers positioned to receive a blade orientedperpendicularly to the long axis of the receptacle.

The flat forward surface of finger 94 bears against the opposite side ofblade 90 under the urging of the spring clip upright 64 pressing againstthe back of the finger 94.

In the left hand side of FIG. 3 a blade is shown inserted into thefingered contact to the left side of the figure and orientedperpendicular to the long axis of the receptacle of FIG. 3.

The left upright 66 of the clip is seen bent into position to bring theprongs 67 and 68 onto either side of the upwardly extending fingers 87and 88 as best seen in FIG. 2.

Referring again to both FIG. 3 in which blades are illustrated in placein the receptacle and to FIG. 2 where the blades are absent, a blade 100brought into position through port 57 in cover 16 spreads blades 87 and88 apart and into spring contact with prongs 67 and 68 of upright 66 ofthe reinforcing U clip. Blade 100 may also press against finger 84 butthis is not necessary to achieve the N EMA contact performance as theblades 87 and 88 as reinforced by spring clip upright 66 achieve thislevel of blade retaining performance.

As is seen at the right hand side of FIG. 3 the straight portion 66 ofthe forked upright of the clip bears against the lower portion of theparallel fingers 106. Accordingly, the clip exerts a first compressivespring pressure on the fingers when a blade such as 90 is in place inthe fingered contact. This is distinct from a second compressive springpressure exerted at right an gles to the first pressure in urging theparallel fingers together when a blade such as 100 is therebetween asseen in the left hand side of FIG. 3.

A novel feature of the present invention is the use of a metal contactof higher conductivity and lower spring compression properties toreceive power blades in two orientations at right angles to each otherin combination with a metal clip of lower conductivity and higher springcompression properties where the reinforcing spring clip acts on thefingered contact to compress the fingers thereof together in twodirections at right angles to each other.

The reinforcing clip may be made from spring steel as for I example SAE1095 and having a Hardness and Temper of Rockwell A 73-75. A strip of0.0l8 mil has been demonstrated satisfactory.

What is claimed is: 1. An electrical contact comprising a contact stripof metal of high conductivity and a low spring properties said striphaving three contact fingers extending up from a common base to providetwo contact slots in T formation therebetween, two fingers beingparallel to the base of the T and on opposite sides thereof a thirdfinger being parallel to the cross member of the T and disposed abovesaid cross member, a spring reinforcing clip for said contact said clipbeing generally U shaped one upright of said U embracing the crossfinger of said contact and having its upper end bent inwardly to bearagainst said cross finger, the other upright being forked at its upperportion and the upper end of said fork being bent inwardly to engage theouter surface of said parallel fingers to add spring bias to resist thespread of said fingers.

1. An electrical contact comprising a contact strip of metal of highconductivity and a low spring properties said strip having three contactfingers extending up from a common base to provide two contact slots inT formation therebetween, two fingers being parallel to the base of theT and on opposite sides thereof a third finger being parallel to thecross member of the T and disposed above said cross member, a springreinforcing clip for said contact said clip being generally U shaped oneupright of said U embracing the cross finger of said contact and havingits upper end bent inwardly to bear against said cross finger, the otherupright being forked at its upper portion and the upper end of said forkbeing bent inwardly to engage the outer surface of said parallel fingersto add spring bias to resist the spread of said fingers.